Recently, there has been a growing consumer demand for resin materials, such as so-called fingernail polishes, toenail polishes, and sculptures, which are applied to nails to decorate or reinforce the nails for the purposes of decorating natural nails or artificial nails that are glued over natural nails or preventing nails from chipping or peeling due to an external force applied during exercises. The mainstream of toughened keratin coating materials used for decoration or reinforcement is a nitrocellulose based lacquer dissolved in an organic solvent to which pigments having various color tones are added. In addition to this, various keratin coating materials are used, for example, an alkyd resin based lacquer containing pigments and plasticizers. These keratin coating materials provide a coating surface exhibiting excellent gloss in a short time after being applied to the keratin of nails and then the solvent being evaporated. Meanwhile, a coating formed on nails can be readily wiped off with an organic solvent such as acetone.
Such keratin coating materials however inevitably contains organic solvents. A problem of the materials is that the user directly inhales evaporating organic solvents during coating. Furthermore, the formed coating cannot be readily removed with water. It must be wiped off with, for example, a large amount of organic solvent, which has a strong odor and an adverse effect on the user's health. Moreover, organic solvents have a risk of decreasing the physiological function of nails and skin. In addition, most organic solvents are flammable and can be significantly dangerous for household use.
Examples of commonly known keratin coating materials include compositions containing non-reactive polymers and compositions containing reactive curable resins. A solvent or diluent contained in a composition containing a non-reactive polymer is evaporated to form a polymer coating. The formation of the coating, which involves no chemical reaction, has advantages in high stability during storage and low physiological irritancy. Unfortunately, a coating formed on the keratin without chemical cross-links cannot be tough and can be peeled off readily by external forces such as scratching.
Meanwhile, a composition containing a reactive curable resin can form a tough coating composed of a chemically cross-linked polymer. The chemical reaction however must proceed under a relatively moderate condition to minimize the effects on human bodies. Consequently, the reaction of a composition prepared in such manner gradually proceeds during storage, which results in poor preservability. Moreover, such a composition causes a physical irritation more significant than that caused by a non-reactive composition since the chemical reaction proceeds on human bodies.
Patent Literature 1 discloses a photo-crosslinkable nail polish composition containing a polymer having ethylenic double bonds and a predetermined amount of free-radical photo-initiator in a physiologically acceptable medium. Examples of the polymer having ethylenic double bonds include ethylenically unsaturated polyesters, polyesters containing (meth)acrylate side groups and/or end groups, polyurethanes and/or polyureas containing (meth)acrylate groups, polyethers containing (meth)acrylate groups, epoxy acrylates, poly (C1-50 alkyl (meth)acrylates) having at least two functional groups containing ethylenic double bonds on the hydrocarbon-based side chains and/or end chains, polyorganosiloxanes containing (meth)acrylate or (meth)acrylamide groups, perfluoropolyethers containing acrylate groups, and dendrimers and hyperbranched polymers containing (meth)acrylate or (meth)acrylamide groups. In addition to these materials, the photo-crosslinkable nail polish composition may include adjuvants and additives commonly used in nail polishes such as pigments or colorants, plasticizers, coalescing agents, preserving agents, waxes, thickeners, fragrances, UV screening agents, cosmetic active agents for nail care, spreading agents, defoaming agents, and dispersants. The technology attempts to solve a toxicity problem of a photo-crosslinkable cosmetic composition by employing reactive components having a sufficiently high molecular mass, instead of highly reactive molecules having a small molecular mass, to prevent them from diffusing towards the neighboring biological substrates. Unfortunately, the toxicity problem is not sufficiently solved and the appearance after curing is not satisfactory.
Patent Literature 2 discloses a solvent-free photocurable nail polish comprising a compound having a polymerizable unsaturated group and a photoinitiator. The compound having a polymerizable unsaturated group refers to a monomer or oligomer having a polymerizable unsaturated group. Examples of the compound include a large number of materials such as polyethylene glycol diacrylate, ethoxy diethylene glycol acrylate, phenoxyethyl acrylate, and phenoxy polyethylene glycol acrylate. In addition to these materials, the solvent-free photocurable nail polish may contain photoinitiating aids, colorants, pearly polishing agents, delustering agents, fragrances, ultraviolet absorbing agents, humectants, defoaming agents, coupling agents, and thixotropic agents. The object of the technology is to provide a solvent-free nail polish. Unfortunately, the polish has a number of adverse effects on human bodies that result from a direct application to human bodies of a compound having a polymerizable unsaturated group, a photoinitiator, and other additives without being diluted due to solvent-free formulation. Another disadvantage of the solvent-free nail polish is nonuniform coating on nails due to its high viscosity.
Patent Literature 3 discloses a nail polish containing a photocurable resin and a coating remover mixed in a nail-polish organic solvent. The photocurable resin used therein is α-hydroxycyclohexyl phenyl ketone and the coating remover is polyester urethane acrylate. In the embodiment of a combination of a base coat agent and a color polish, further used are triethylene glycol dimethacrylate, polyether-modified silicone oil, epoxy methacrylate, and epoxy acrylate. The technology is effective in drying instantly and in being able to peel off without damaging the surface of natural nails. Unfortunately, the polish, which is nonaqueous, does not exhibit sufficient safety to human bodies and thus requires careful attention during handling.
Patent Literature 4 discloses an aqueous nail polish composed of aqueous pigment dispersion and aqueous resin emulsion, the dispersion containing a surfactant and/or an addition polymer of ethylenically unsaturated monomers including an α, β-mono-ethylenically unsaturated acid; and a method of making the polish. The aqueous resin emulsion used therein is, for example, prepared by polymerization of a monomer with a reactive surfactant, the monomer is selected from the group consisting of α, β-ethylenically unsaturated carboxylic acid, methacrylic acid ester, acrylic acid ester, and styrene. Patent Literature 5 discloses an aqueous nail polish containing a resin prepared by polymerization of a monomer with a reactive surfactant, the monomer is selected from the group consisting of α, β-ethylenically unsaturated carboxylic acid, methacrylic acid ester, acrylic acid ester, and styrene. These nail polishes may include, for example, pH regulators, pigments, dyes, dispersing aids, medicaments, ultraviolet absorbing agents, disinfectants, antiseptics, fragrances, plasticizers such as glycolic coating-forming agents, coating-smoothing agents, and thickeners. These nail polishes, which are aqueous, pose no risk such as health impairment or degradation of nails. Moreover, they provide a coating having high adhesion to nails, gloss, and color tone, and the formed coating has high water resistance. Unfortunately, these aqueous nail polishes, which contain non-reactive polymers as mentioned above, have problems of insufficient adhesion to nails and of peeling off readily by an external force such as scratching.
Patent Literature 6 discloses an aqueous nail polish containing at least two different acrylic polymer emulsions having a difference in glass transition temperature therebetween of 10° C. or more. In addition to these materials, the aqueous nail polish may contain, for example, coating-forming aids, plasticizers, pigments, dyes, antiseptics, fragrances, and thickeners. Examples of the coating-forming aids and plasticizers include an extremely large number of materials such as ethylene glycol, propylene glycol, pentaerythritol, glycerol, liquid paraffin, chlorinated paraffin, and machine oil. Compared to aqueous nail polishes containing merely an acrylic polymer emulsion, the aqueous nail polish, which contains at least two different predetermined acrylic polymer emulsions, exhibits somewhat improved gloss, adhesion, and coating hardness. Unfortunately, the endurances such as adhesion, scratch resistance, and toughness of coating are still unsatisfactory.
Patent Literature 7 discloses an aqueous nail polish containing an aqueous emulsion of a self-emulsifiable vinyl polymer and a cellulose derivative. In addition to these materials, the aqueous nail polish may contain, for example, plasticizers, coating-forming aids, pigments, thickeners, dyes, antiseptics, and fragrances. The aqueous nail polish has superior properties such as adhesion, scratch resistance, and water resistance, which leads to excellent gloss and long lastingness. Unfortunately, the water resistance is still unsatisfactory and the polish cannot be used practically due to a drawback of peeling off readily during daily use.